Radio Communication Terminal and Communication Method

ABSTRACT

A radio communication terminal, being used in a radio communication systems in which the transmission rate varies depending on radio wave conditions and communication statuses of other users, comprises a reception module which receives packets transmitted by a base station in an idle state of the radio communication terminal, a signal processing module which estimates a transmission rate available in communication based on the packets received by the reception module, and a display module which displays information indicating the transmission rate estimated by the signal processing module.

BACKGROUND OF THE INVENTION

The present invention relates to a radio communication terminal oraccess terminal to be used in a radio communication system and acommunication method for the radio communication terminal.

Radio communication systems for communicating are being rapidlyintroduced to various fields in recent years. Especially, CDMA (CodeDivision Multiple Access) radio communication systems, communicatinginformation (audio information, etc.) by code division multiplexing theinformation by use of a plurality of spread codes, have recently becomewidespread, by which high-speed communication irrespective of time,place and the party has become possible. As a type of CDMA, 1xEV-DO (1xEVolution Data Only) radio communication system is known, for example.Since 1xEV-DO employs variable bit rate communication (best effort radiocommunication system), higher transmission rate is more beneficial tothe users.

However, in best effort radio communication systems like 1xEV-DO, thetransmission rate can not arbitrarily be designated and set by the userbut varies depending on conditions of radio waves. Thus, techniques foreasily checking the radio wave conditions and controlling thecommunication method depending on the radio wave conditions arerequired. For example, a mobile terminal disclosed in JP-A-5-207544estimates quality of communication (communication quality) based onelectric field intensity information, noise information, etc. concerningreceived radio signals and previously obtained communication qualitymeasurement/judgment results, and displays availability/unavailabilityof voice communication, availability/unavailability of datacommunication, maximum data transmission rate (when data communicationis available), etc. on its display screen. In a radio communicationsystem disclosed in JP-A-2003-125440, a control station (whichdetermines a radio channel to be used for radio communication between amobile station and a base station) calculates throughput of each radiochannel that can be allocated to a mobile station (whose transmissionrate varies depending on the allocated radio channel) and allocates asuitable radio channel to the mobile station based on the calculatedthroughput.

In such communication systems, a terminal can move from a cell (an areacovered by radio waves transmitted by a base station) to another cellwhile communicating with a base station of each cell, therefore, atechnique called “handover” or “handoff”, for maintaining thecommunication even when the terminal moves across cell borders, becomesnecessary. In CDMA radio communication systems, a technique called “softhandover” or “soft handoff” is used, in which a mobile terminalsimultaneously communicates with a plurality of base stations and thecommunication is maintained by selecting a base station in the bestcommunication status from the base stations simultaneously communicatingwith the mobile terminal (see 3GPP TR25.832 Chapter 5.2 and 3GPP2A.S0003-A (Version 2.0) Chapter 5.4, for example).

SUMMARY OF THE INVENTION

As described above, while higher transmission rate is more beneficial tothe users in best effort radio communication systems such as 1xEV-DO,the transmission rate can not be arbitrarily designated by the user butchanges depending on the radio wave conditions, communication statusesof other users, etc. For example, an increase in the number of terminalsexisting in the cell, application software used by the terminal, etc.can also deteriorate the transmission rate. Thus, even in acommunication environment giving high reception intensity, a hightransmission rate can not be expected in cases where high-capacity datatransmission is being done by a plurality of terminals in the cell.

Therefore, users of such radio communication systems (with thetransmission rate varying depending on the radio wave conditions,communication statuses of other users, etc.) will soon hope to beinformed of the highest transmission rate available or attainable in thecurrent environment or conditions.

However, in the above techniques described in JP-A-5-207544 andJP-A-2003-125440, the judgment of communication quality or thecalculation of throughput requires actual communication, affecting radiocommunication of other users (e.g. deterioration of communicationquality). Thus, it can be hardly said that such techniques are capableof obtaining the currently optimum transmission rate (throughput) andare convenient to the system provider and the users.

Further, in a radio communication system with the transmission ratevarying according to the radio wave conditions and the communicationstatuses of other users, it is desired that a terminal carrying out thesoft handover can select a base station realizing the highest throughputin the current communication environment.

However, since the soft handover technique stipulated in theaforementioned documents (3GPP TR25.832 Chapter 5.2 and 3GPP2 A.S0003-A(Version 2.0) Chapter 5.4, for example) executes the switching of basestations by estimating the communication quality mainly based on theelectric field intensity, data communication is carried out necessarilybelow the highest transmission rate that is actually attainable. Suchsystems are not attractive to system providers and users expecting tooffer and enjoy information communication capability at the maximumtransmission rate.

It is therefore the primary object of the present invention to provide aradio communication terminal capable of estimating or letting the userknow the maximum transmission rate available in actual communication(expected throughput) without the need of actually communicating (in theidle state of the terminal) in a radio communication system with thetransmission rate varying depending on the radio wave conditions and thecommunication statuses of other users.

Another object of the present invention is to provide a radiocommunication terminal capable of carrying out radio communication byselecting a base station that can deliver the maximum throughput in aradio communication system with the transmission rate varying dependingon the radio wave conditions and the communication statuses of otherusers.

In order to attain the above object, a radio communication terminal inaccordance with the present invention receives packets from a pluralityof base stations in its idle state, estimates a transmission rate(expected throughput) available for communication based on informationcontained in the packets received from each base stations, and selects asector that gives the highest expected throughput.

Each packet is composed of a broadcast message area and a communicationinformation area (traffic data area), and each of the areas is composedof a plurality of slots as units of time division. Each slot of thebroadcast message area and the communication information area contains apilot signal, and information indicating the number of radiocommunication terminals communicating in the sector is stored in a slotof the broadcast message area.

The radio communication terminal of the present invention obtains anexpected throughput for each base station based on a requestedtransmission rate (requested of each base station) estimated from thepilot signal, the aforementioned number of terminals, and the number ofused data slots and the number of idle slots obtained from thecommunication information area, and displays the highest one of theexpected throughputs on a display module, by which communication withthe base station corresponding to the highest expected throughputbecomes possible when the terminal conducts actual communication.

By the present invention, the expected throughput can be estimated inthe idle state of the radio communication terminal and displayed on thedisplay module of the terminal. Therefore, the user is allowed to learnthe expected throughput without the need of actually carrying outcommunication.

Further, by the selection of the sector capable of exhibiting highthroughput, highly efficient data communication is made possible.

Referring now to the drawings, a description will be given in detail ofpreferred embodiments in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become moreapparent from the consideration of the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing the overall composition of aradio communication system in accordance with an embodiment of thepresent invention;

FIG. 2 is a block diagram showing an example of the composition of aradio communication terminal in accordance with the present invention;

FIG. 3 is a schematic diagram showing the composition of a packet;

FIG. 4 is a flow chart showing a process conducted by the radiocommunication terminal for determining a “selected sector”;

FIG. 5 is a flow chart showing the details of a process conducted by theradio communication terminal for estimating an expected throughput whenthe terminal is in its idle state;

FIG. 6 is a table showing the contents of a table which is used fordetermining a requested transmission rate;

FIG. 7 is a flow chart showing a process conducted by the radiocommunication terminal for obtaining the number of used data slots andthe number of idle slots;

FIG. 8 is a schematic diagram showing a mathematical formula forobtaining the expected throughput;

FIG. 9 is a schematic diagram showing an example of display on a displayunit of a conventional radio communication terminal;

FIG. 10 is a schematic diagram showing an example of display of theexpected throughput on a display unit of the terminal of the presentinvention;

FIG. 11 is a schematic diagram showing another example of display of theexpected throughput on a display unit of the terminal of the presentinvention;

FIGS. 12 and 13 are schematic block diagrams showing the overallcomposition of the radio communication system for explaining theoperation of the radio communication terminal using concrete parameters;

FIG. 14 is a table showing an example of slot assignment; and

FIG. 15 is a table showing results of a process for obtaining theexpected throughput.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a schematic block diagram showing the overall composition of aradio communication system in accordance with an embodiment of thepresent invention. Each radio communication terminal (100-1, 100-2, . .. ) establishes a radio communication channel with a radio communicationapparatus (300-1). In this embodiment, a radio communication areamanaged by the base station 300-1 is referred to as a “sector” 200-1, inwhich a plurality of terminals (100-1, 100-2, . . . ) are connectable tothe base station 300-1. Other sectors 200-2, 200-3, 200-4, are alsodefined similarly. In order to realize the handover between sectors,adjacent sectors (e.g. sectors 200-1 and 200-2) overlap with each other.

The base stations 300-1 and 300-2 are connected by wire to a basestation controller 400-1. Similarly, the base stations 300-3 and 300-4are connected by wire to a base station controller 400-2.

The base station controllers 400-1 and 400-2 are both connected by wireto a network 500 such as the Internet or a public communicationsnetwork.

Each terminal receives packets 1000 from a base station via the radiocommunication channel established between the base station and theterminal. While details will be described later, the packet 1000contains communication data or communication information (hereafter,referred to as “traffic data”) 1100 actually handled by the user andbroadcast messages 1050 containing a variety of information (status ofthe base station, etc.) necessary for the connection of the terminalwith the base station. The broadcast message 1050 and the traffic data1100 are both composed of a plurality of “slots” (units of timedivision), and each slot contains a pilot signal 1200. Each terminalmeasures reception intensity (reception power) based on the pilot signalreceived from the base station and thereby estimates a characteristicvalue regarding the communication quality. A ratio called C/I or CIR(Carrier to Interference Power Ratio), as a signal power ratio between adesired signal from the base station and other received signals(interference power), is generally used as a parameter regarding thecommunication quality. The packet 1000 includes a traffic data area 1100for storing the communication data of the user, in which data for eachuser are stored in units of slots. When there is no communication datato be stored in a slot, the slot is transmitted in an idle or vacantstate (hereinafter referred to as an “idle slot”).

In order to perform data communication, the terminal 100-1 first sends aconnection request to the base station 300-1. The base station 300-1which received the connection request from the terminal 100-1 firstestablishes a communication channel with the base station controller400-1 and then assigns radio resources to the terminal 100-1, by which aradio communication channel between the terminal 100-1 and the basestation 300-1 is established. For the radio resource assignment processand/or the communication with the base station controller or a networkon a still higher level, specific functions for authentication, billing(charging), etc. may also be employed.

The terminal 100-1, having established the radio communication channeland ready for data communication, estimates a maximum transmission rateallowing data reception in its communication environment, and requeststhe base station 300-1 to employ the maximum transmission rate. Inresponse to the request, the base station 300-1 carries out datatransmission to the terminal 100-1 at the requested transmission rate.The terminal 100-1 may use a table like that shown in FIG. 6 for theestimation of the transmission rate to be requested. Details of thetable will be explained later.

FIG. 2 is a block diagram showing an example of the composition of theradio communication terminal in accordance with the present invention.Each terminal (100-1, 100-2, . . . , 110-1, . . . ) includes an antenna170, a transmission/reception unit 110, a signal processing unit 120, anI/O control unit 130, a peripheral unit 140, a processor 150, and amemory (storage unit) 160.

The peripheral unit 140 is provided with an input unit 140-1 having keysfor inputting data and instructions (for call origination, etc.), adisplay unit 140-2 for displaying expected throughput, etc., and aspeaker 140-3. The input unit 140-1 may also employ a touch panel, mousepointer, microphone, etc. Although not shown in FIG. 2, an output unitfor printing out the information displayed on the display unit 140-2(estimation result, etc.) may also be provided to the peripheral unit140.

The transmission/reception unit 110 receives packets (containing thetraffic data 1100 and the broadcast messages 1050) from the base stationthrough the antenna 170, while transmitting packets to the base stationby the antenna 170. For the communication with the base station, thetransmission/reception unit 110 conducts modulation/demodulationprocesses according to PSK (Phase Shift Keying), etc.

The signal processing unit 120 estimates the throughput (expectedthroughput) based on the broadcast message 1050 and the traffic data1100 contained in the received packets and thereby determines a“selected sector” (a sector selected by the terminal for communication).The expected throughput obtained by the signal processing unit 120 isdisplayed on the display unit 140-2.

The memory 160 stores control programs (for the estimation of theexpected throughput, determination of the selected sector, connection toa base station in the selected sector) to be executed by the processor150.

FIG. 3 is a schematic diagram showing the composition of the packet1000. The packet 1000 is partitioned into two areas: a broadcast messagearea 1050 and a traffic data (communication information) area 1100. Thebroadcast message area 1050 and the traffic data area 1100 are bothcomposed of a plurality of slots as units of time division. In thisembodiment, the duration of each slot is 1/600 s (approximately 1.67ms). The broadcast message area 1050 is composed of 8 slots (or 16slots), while the traffic data area 1100 is composed of 248 slots (or240 slots). Each base station packs necessary information in the packet1000 (as a cycle of approximately 426.67 ms composed of 256 slots), andcontinuously transmits the packets to the terminals. Incidentally, eachslot is composed of a pair of half slots, and the pilot signal 1200 isstored at the center of each half slot.

Broadcast message data 1060 in the broadcast message area 1050 of thepacket transmitted by a base station includes, for example, informationon the number of terminals connected to the base station.

The traffic data area 1100 contains communication data (communicationinformation) addressed to a plurality of terminals. Each slot of thetraffic data area 1100 stores communication data addressed to aparticular terminal, and the assignment of the slots to the terminals isdetermined by the base station transmitting the packet. Slots that areassigned to no terminal become the aforementioned idle slots containingno communication data. The data stored in each slot and addressed to aterminal have been encoded by the base station by use of a key that isunique to the terminal. The base station has already informed theterminal about the key(s) as one of the radio resources (when theterminal established the radio communication channel with the basestation). The terminal which received the encoded data from the basestation decodes the data using the key and thereby recognizes the dataas correct data.

FIG. 4 is a flow chart showing a process for determining the “selectedsector”. First, various data stored in the memory 160 is initialized(step 802). In the step 802 of FIG. 4, the symbol “T” denotes theexpected throughput in the sector where the terminal is going toestablish (or has established) a radio communication channel. The symbol“n” denotes a numerical value used in the flow for the sake ofconvenience. In this embodiment, “n” is a logical number assigned toeach sector from which the terminal can receive the pilot signal 1200.The terminal properly reassigns the logical numbers “n” when a changeoccurred in the combination of the sectors from which the pilot signal1200 can be received. As a rule for the logical number assignment,nonnegative integers are assigned to the sectors in consecutive orderstarting from a certain smallest number. The symbol “S” denotes thenumber of a sector whose expected throughput is the highest. The symbol“N” denotes the number of “receivable sectors” (sectors from which thepilot signal 1200 can be received) estimated by the terminal based onthe pilot signal 1200 received from a plurality of base stations. Thenumber N changes when the number of “receivable sectors” changed due tothe change of environment (movement of the terminal, etc.). After theinitializing step 802 is finished, in the step 803, the signalprocessing unit 120 judges whether or not the process of FIG. 4 has beenconducted for all of the N receivable sectors from which the pilotsignal 1200 can be received. If there remains an unprocessed sector n(YES in the step 803), the terminal receives packets 1000 from thesector n, obtains data necessary for the estimation of the expectedthroughput, and estimates the expected throughput Tn (step 804).

Subsequently, the signal processing unit 120 judges whether or not theexpected throughput Tn of the sector n is higher than the expectedthroughput T of the currently selected sector (step 805). If the newlyobtained expected throughput Tn is higher (YES in the step 805), thesignal processing unit 120 changes the selected sector to the sector n.

Steps 806-810 are the process for changing the selected sector, in whichthe terminal sends a sector change request to the base station (step807) if the terminal is in its active state (call connected state) (YESin step 806). Subsequently, the signal processing unit 120 executes theselected sector changing process and thereby stores information on thenew sector (corresponding to the higher expected throughput) in thememory 160 (step 808), updates the expected throughput stored in thememory 160 into Tn (step 809), and changes the display into thatcorresponding to the new expected throughput Tn (step 810).

Meanwhile, if the processing unit 120 decides the terminal being not inthe active state (NO in the step 806), the signal processing unit 120directly proceeds to the step 808 and executes the selected sectorchanging process (steps 808-810). After the selected sector changingprocess is finished, the number n is incremented by 1 (step 811) and theprocess is returned to the step 803. By the repetition of theabove-mentioned steps 803-810, the estimation of the expected throughputis conducted for all the sectors from which the pilot signal 1200 can bereceived.

After the above process for the estimation of expected throughput andthe determination of selected sector is completed for all the receivablesectors by the reception of the pilot signal 1200, the number n isinitialized to 0 (step 812) and thereafter the process for theestimation of expected throughput and the determination of selectedsector is executed again for all the receivable sectors (from which thepilot signal 1200 can be received). By the repetition of the aboveprocess, the signal processing unit 120 can select a sector giving thehighest expected throughput.

Incidentally, while all the receivable sectors (from which the pilotsignal 1200 can be received) are regarded as candidates for the“selected sector” in this embodiment, the candidates may be restrictedto sectors fulfilling a proper condition (for example, sectors fromwhich the pilot signal 1200 can be received with radio field intensityhigher than a threshold intensity).

FIG. 5 is a flow chart showing the details of a process for estimatingthe expected throughput when the terminal is in its idle state (with nocall connection). The signal processing unit 120 of the terminalreceives packets 1000 transmitted by the base station via thetransmission/reception unit 110 (steps 701 and 702), extracts pilotsignals 1200 from slots of the received packet 100 s, and therebyestimates the C/I ratio. From the estimated C/I ratio and a table storedin the memory 160 which will be explained later, the signal processingunit 120 determines the transmission rate to be requested of the basestation (step 703).

The signal processing unit 120 also obtains the number of terminalconnected to (communicating with) the base station (sender of the packet1000) from the broadcast message 1050 contained in the packet 1000 (step704). The number of the connected terminals can be obtained from, forexample, the Forward Traffic Valid bit contained in the Quick Configmessage. Further, the signal processing unit 120 counts the number ofdata slots being used and the number of idle slots by referring to thetraffic data 1100 (step 705). Based on the above information (requestedtransmission rate, the number of connected terminals, the number of useddata slots, and the number of idle slots), the signal processing unit120 estimates the expected throughput in the sector (step 706).

Thereafter, the signal processing unit 120 determines a sector thatgives the highest expected throughput by the aforementioned processshown in FIG. 4 (step 707) and instructs the display unit 140-2 todisplay the highest expected throughput (step 708). In response to theinstruction, the display unit 140-2 displays the expected throughput(step 709). When a change occurs to the expected throughput or theselected sector, the expected throughput displayed on the display unit140-2 is updated by the process of FIG. 5. When no change occurs to theexpected throughput nor the selected sector, the expected throughput onthe display unit 140-2 remains constant.

FIG. 6 shows the contents of a table 60 which is used for determiningthe requested transmission rate. In the table 60 held in the memory 160,a plurality of C/I ratios 60-1 and corresponding transmission rates 60-2are prestored.

In this embodiment, the terminal obtains the C/I ratio from the pilotsignals contained in the received packets, searches the table 60 withthe C/I ratio, and thereby determines the transmission rate to berequested of the base station that transmitted the packets.

FIG. 7 is a flow chart showing the process for obtaining the number ofused data slots and the number of idle slots. In radio communicationsystems like 1xEV-DO, each slot of the traffic data area 1100 storesdata that have been encoded by spread code uniquely assigned to eachterminal as the key, therefore each terminal can not directly recognizethe data as it is. Further, since the assignment of slots to theterminals is determined by the base station according to algorithmconsidering the transmission rates requested by the terminals, eachterminal can not immediately judge to which terminal each slot has beenaddressed (or whether or not each slot is an idle slot addressed to noterminal). Thus, in order to acquire data addressed to itself, eachterminal successively despreads the data stored in each slot using thespread code key assigned to itself by the base station, judges whetheror not the despread data has autocorrelation, and extracts dataexclusively from slots having the autocorrelation. Therefore, thefollowing process of FIG. 7 becomes necessary for judging whether eachslot is an idle slot or not and count the numbers of used data slots andidle slots in a prescribed time period.

First, the terminal initializes various data in order to count thenumber of idle slots (step 902). In the step 902 shown in FIG. 7, thesymbol “s” denotes a counter value indicating the number of countedslots, “p” denotes a counter value indicating the number of idle slotsincluded in the counted slots, “M” denotes the upper limit of the spreadcode key (63 in 1xEV-DO) which also means the upper limit of the keyemployed for the despreading of each slot, and “S” denotes the totalnumber of slots included in a prescribed time period. The length of theprescribed time period can arbitrarily be set and varied.

After the initialization of various data, a number “n” designating a keyto be used for the despreading is first set to the lower limit of thespread code key (set to 5 in 1xEV-DO) (step 903). When the number s ofcounted slots does not exceed the total number S of slots included inthe prescribed time period (YES in step 904) and the spread code key ndoes not exceed the upper limit M (YES in step 905), the signalprocessing unit 120 despreads a slot of the traffic data area 1100 usingthe spread code key n as the key (step 906).

If the data obtained by the despreading has autocorrelation (YES in step907), it means that the slot stores data addressed to a terminal towhich the spread code key n has been assigned. In this case, the signalprocessing unit 120 judges that the slot is not an idle slot, incrementsthe counter value s indicating the number of counted slots (step 910),and then repeats the process for the next slot. On the other hand, ifthe despread data does not have autocorrelation (NO in step 907), thesignal processing unit 120 increments the number n to designate the nextspread code key (step 908) and executes the process from the step 905using the next spread code key.

If the spread code key n has become the upper limit M or more (NO in thestep 905), that is, if no autocorrelation has been found in spite of thedespreading of the slot by use of all the spread code keys, it meansthat the slot has been addressed to no user (no terminal). In this case,the signal processing unit 120 increments both the counter value p(indicating the number of idle slots) and the counter value s(indicating the number of counted slots) (step 909). By repeating theabove process for all the slots in the prescribed time period, thenumber of idle slots can be obtained.

By the above process, the number s of counted slots, the number p ofidle slots, and the number s-p of used data slots (data slots storingdata addressed to terminals) are obtained (step 911).

FIG. 8 is a schematic diagram showing a mathematical formula forobtaining the expected throughput. The formula is based on the followingconcept.

First of all, the expected throughput 601 is dependent not only on thetransmission rate 600 that the terminal requested of the base stationbut also on the number of slots assigned to the terminal by the basestation, since the base station is allowed in 1xEV-DO to pack data ineach slot changing the modulating method (causing a change in the datatransmission rate). Thereby the base station transmits data necessarilyat the transmission rate requested by the terminal. Thus, the size ofdate received by the terminal is obtained as the product of therequested transmission rate and the number of assigned slots (slotsassigned to the terminal). For example, when the number of slotsassigned to the terminal for a certain time period is small, the amountof data received by the terminal in the time period becomes small andthe throughput at the terminal becomes low. On the other hand, thethroughput at the terminal becomes high when a large number of slots areassigned to the terminal for a certain time period. Incidentally, themaximum value of the throughput is equal to the transmission rate thatthe terminal requested of the base station.

However, the terminal can not exactly grasp the number of slots assignedto itself by the base station because the base station changes the slotassignment to each user (each terminal) depending on the number ofcommunicating terminals, data traffic, radio wave conditions at eachterminal, etc.

Therefore, the number of slots assigned by the base station to theterminal is estimated as below based on the numbers of used data slotsand idle slots obtained by the process of FIG. 7. First, it is assumedthat the base station assigns all the idle slots 603 to the terminalunder consideration. Meanwhile, an average number 607 of slots assignedby the base station to the terminal is obtained as the number 604 ofused data slots divided by the number 606 of terminals, in which thenumber 606 of terminals is obtained by adding 1 (the terminal itself) tothe number 605 of communicating terminals (communicating users) obtainedby the step 704 of FIG. 5. The number 608 of slots assigned to theterminal is assumed to be the sum of the number 603 of idle slots andthe average number 607 of slots assigned by the base station to theterminal.

Therefore, the expected throughput of data transmitted from the basestation to the terminal can be estimated by multiplying the requestedtransmission rate 602 (obtained in FIG. 6) by a ratio 610 that isobtained by dividing the number 608 of slots assigned to the terminal bythe total number 609 of slots (the number of used data slots and thenumber of idle slots added together).

The present invention is characterized by the method for obtaining theexpected throughput, based not only on the transmission rate that theterminal requested of the base station but also on the number ofcommunicating (connected) terminals and the expected number of slotsassigned to the terminal.

FIG. 9 is a schematic diagram showing an example of display on a displayunit of a conventional radio communication terminal, in which electricfield intensity (power) of a radio wave received from the base station(showing voice quality) is digitally indicated by the number of barsbeside the antenna icon.

However, high reception power and C/I ratio do not guarantee highthroughput in the best effort radio communication system as mentionedabove. FIGS. 10 and 11 show examples of display on the display unit140-2 of the terminal in accordance with the present invention,indicating the expected throughput.

In the example of FIG. 10, the expected throughput obtained by theformula of FIG. 8 is displayed in the form of a peak level meter foreasy reading by the user. By displaying the peak level (momentarymaximum throughput) for a certain time period, the user can recognizewhether the expected throughput is on the increase or decrease at aglance.

In the example of FIG. 11, the peak level meter of FIG. 10 is replacedwith bucket symbols. The number of buckets is increased or decreasedaccording to the increase/decrease of the expected throughput.

Incidentally, while FIGS. 10 and 11 have been shown as typical examplesof symbols for indicating the expected throughput, other symbols are ofcourse possible as long as the expected throughput is recognizable.

When the terminal is in the active state and during data communication,actual throughput (size of transferred data measured in certain unittime), the number 605 of terminals communicating in the selected sector,etc. may also be displayed on the display unit 140-2.

Further, since the above function in accordance with the presentinvention increases power consumption of the terminal and decreasesmaximum duration of data communication, the peripheral unit 140 isprovided with an interface (switch, key, etc.) for letting the user turnthe function ON and OFF. When the function of the present invention isOFF, the terminal may select a sector that gives the highest radio fieldintensity of the pilot signal. By the ON/OFF function, power consumptioncan be reduced when the user does not need the display of the expectedthroughput.

In the following, the operation of the terminal will be explained indetail using concrete parameters. As shown in FIG. 14, thirty terminalsare executing data communication in a sector 200-1 (sector #1), in whicha base station 300-1 is communicating with the thirty terminalsassigning them 800 slots when the number of slots transmitted in aprescribed time period is 1000 (S=1000 in FIG. 7). Meanwhile, threeterminals are executing data communication in a sector 200-2, in which abase station 300-2 is communicating with the three terminals assigningthem 400 slots when the number of slots transmitted in a prescribed timeperiod is 1000.

First, the estimation of the throughput when a terminal 100-3 is in thesector 200-1 will be explained referring to FIG. 12. Since the C/I ratioobtained from the pilot signal 1200 is 3 dB, the terminal 100-3estimates the requested transmission rate as 1228.8 kbit/s by referringto the table 60 of FIG. 6. Subsequently, the terminal 100-3 acquires thenumber of communicating terminals (connected terminals) from thebroadcast message data 1060 and counts the number 603 of idle slots andthe number 604 of used data slots according to the flow chart of FIG. 7,by which the terminal 100-3 finds out that the number 603 of idle slotsis 200 out of 1000 slots (in the case where the total number S of slotsincluded in the prescribed time period is 1000), the number 604 of useddata slots is 800, and the number of terminals communicating in thesector is 30. By substituting the values into the formula of FIG. 8, theexpected throughput in the sector #1 (sector 200-1) is obtained as 277.5kbit/s. In this case, the throughput is displayed on the display unit140-2 since the packets 1000 are all received from the base station300-1 only. The user of the terminal 100-3 learns the expectedthroughput (throughput that is expected to be attained in actualcommunication) by seeing the display. When a call is originated, theterminal 100-3 sends a connection request to the base station 300-1.

However, if the terminal 100-3 moves into the position shown in FIG. 13(in the overlapping area of the sectors 200-1 and 200-2) before startingcommunication, the terminal 100-3 receives packets 1000 from both thebase stations 300-1 and 300-2. In this case, the terminal 100-3calculates expected throughputs for two cases: communication with thebase station 300-1 and communication with the base station 300-2, anddisplays the highest one of the expected throughputs on the display unit140-2.

For the sector 200-1, the terminal 100-3 obtains the expected throughputas 277.5 kbit/s in the same way as the above explanation. For the sector200-2, since the C/I ratio obtained from the pilot signal 1200 is −1 dB,the terminal 100-3 first estimates the requested transmission rate as614.4 kbit/s by referring to the table 60 of FIG. 6. Subsequently, theterminal 100-3 acquires the number of communicating terminals from thebroadcast message data 1060 and counts the number 603 of idle slots andthe number 604 of used data slots according to the flow chart of FIG. 7,by which the terminal 100-3 finds out that the number 603 of idle slotsis 600 out of 1000 slots (in the case where S=1000), the number 604 ofused data slots is 400, and the number of terminals communicating in thesector 200-2 is 3. By substituting the values into the formula of FIG.8, the expected throughput in the sector #2 (sector 200-2) is obtainedas 430.1 kbit/s.

Results of the above process for obtaining the expected throughput areshown in FIG. 15, in which the expected throughput in the sector #2 ishigher. In this case, the expected throughput of the sector 200-2 isdisplayed on the display unit 140-2 of the terminal 100-3, by which theuser learns the expected throughput (throughput that is expected to beattained in actual communication). When a call is originated, theterminal 100-3 executes a process for establishing connection with thebase station 300-2. It is also possible to display both the throughputin the sector 200-1 and the throughput in the sector 200-2 and carry outcommunication by selecting a base station in a sector selected.

As described above, by the radio communication terminal and thecommunication method in accordance with the embodiment of the presentinvention, the expected throughput can be estimated by each terminal.Thus, in cases where high-throughput data communication is necessary,the expected throughput can be used as major information for judgingwhether the data communication should be started or not, by which theterminal's degree of freedom in data communication is enhanced andservice quality can be improved.

By the employment of the interface (switch, key, etc.) for letting theuser turn the above functions ON and OFF, the flexibility of sectorselection is increased and thereby further improvement of servicequality can be expected.

From the viewpoint of infrastructure, the estimation of expectedthroughput and the selection of sector in accordance with the presentinvention can be realized only by adding the above functions toterminals with relatively low remodeling costs. The present inventionprovides an economical approach involving almost no alteration of theoperation of network devices (base stations, etc. requiring highremodeling costs).

Further, the selection of base station and the establishment ofcommunication channel are carried out on the initiative of theterminals, which contributes to load balancing for the network devicessuch as base stations.

Incidentally, while the estimation of the expected throughput and thedetermination of the selected sector were carried out by the signalprocessing unit 120 shown in FIG. 2, the processes may also be conductedby the processor 150.

While the above explanation has been given assuming the terminal is inthe idle state, the present invention is applicable regardless ofwhether the terminal is in the idle state or in the active state (callconnected state). For example, assuming that the terminal 100-3 has beencall connected with the base station 300-1 in the sector 200-1, theterminal 100-3 is connected to the base station 300-2 in the sector200-2 if the sector 200-2 gives a higher expected throughput. Theterminal 100-3 sends a connection request to the base station 300-2, andin response to an output of the base station 300-2 receiving theconnection request, the connection is switched to the base station300-2. By this embodiment, the terminal continues selecting a moresuitable sector capable of delivering a higher transmission rate at thecurrent position, by which erroneous continuation of low speed datacommunication with the presence of a more suitable sector can be avoidedand thereby highly efficient data communication can be realized.

The embodiments explained above is applicable to radio communicationsystems (1xEV-DO, etc.) in which the transmission rate changes dependingon radio wave conditions and communication statuses of other users.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A radio communication terminal in a system wherein each of data foreach of radio communication terminals is coded based on each of codekeys assigned to each of the radio communication terminals, each of thecoded data is stored into each of slots, a base station transmitsinformation in units of packet including the slots, the number of slotsincluded in the packet is predetermined, and each of the slots has acommunication information area which stores necessary variousinformation for indicating a state of the base station and for which theradio communication terminal connects to the base station, the radiocommunication terminal comprising: a receiving unit which receives apacket transmitted from the base station when a communication path tothe base station is not established before a call connection request istransmitted to the base station; a storing unit which stores the codekeys each of which is assigned to each of the radio communicationterminals; and a measuring unit which measures whether each of all slotsin the received packet is an unused slot or a used slot by using thecoded keys which are stored in the storing unit and each of which isassigned to each the radio communication terminals, wherein atransmission rate is calculated based on information obtained from thenumber of used slots, the number of unused slots and each communicationinformation included in each of the slots before the communication pathis established, and the transmission rate is a rate to be actuallyassigned when the communication path to the base station is establishedafter the call connection request is transmitted to the base station. 2.The radio communication terminal according to claim 1, furthercomprising a display unit, wherein the transmission rate to actually beassigned which is calculated before the communication path isestablished is displayed on the display unit.
 3. A radio communicationterminal in a system wherein each of data for each of radiocommunication terminals is coded based on each of code keys assigned toeach of the radio communication terminals, each of the coded data isstored into each of slots, a base station transmits information in unitsof packet including the slots, the number of slots included in thepacket is predetermined, and each of the slots has a communicationinformation area which stores necessary various information forindicating a state of the base station and for which the radiocommunication terminal connects to the base station, the radiocommunication terminal comprising: a receiving unit which receives apacket transmitted from the base station when a communication path tothe base station is not established before a call connection request istransmitted to the base station; a storing unit which stores the codekeys each of which is assigned to each of the radio communicationterminals; a measuring unit which measures whether each of all slots inthe received packet is an unused slot or a used slot by using the codedkeys which are stored in the storing unit and each of which is assignedto each of the radio communication terminals; a determining unit whichmeasures a parameter regarding a signal quality based on a pilot signalof each of the slots and which determines a request transmission ratefor the base station based on the measured parameter; and an acquiringunit which acquires information, included in the communicationinformation area, regarding the number of mobile communication terminalsconnected to the base station, wherein a transmission rate is calculatedbased on the number of used slots, the number of unused slots, therequest transmission rate and the number of radio communicationterminals connected to the base station before the communication path isestablished, and the transmission rate is a rate to be expected when thecommunication path to the base station is established after the callconnection request is transmitted to the base station.
 4. The radiocommunication terminal according to claim 1, further comprising adisplay unit, wherein the transmission rate to actually be assignedwhich is calculated before the communication path is established isdisplayed on the display unit.
 5. A communication method in a systemwherein each of data for each of radio communication terminals is codedbased on each of code keys assigned to each of the radio communicationterminals, each of the coded data is stored into each of slots, a basestation transmits information in units of packet including the slots,the number of slots included in the packet is predetermined, and each ofthe slots has a communication information area which stores necessaryvarious information for indicating a state of the base station and forwhich the radio communication terminal connects to the base station, thecommunication method comprising: storing the code keys each of which isassigned to each of the radio communication terminals; receiving apacket transmitted from the base station when a communication path tothe base station is not established before a call connection request istransmitted to the base station; measuring whether each of all slots inthe received packet is an unused slot or a used slot by using the codedkeys each of which is assigned to each of the radio communicationterminals; and calculating a transmission rate based on informationobtained from the number of used slots, the number of unused slots andeach communication information included in each of the slots before thecommunication path is established, and the transmission rate is a rateto be actually assigned when the communication path to the base stationis established after the call connection request is transmitted to thebase station.
 6. The communication method according to claim 5, furthercomprising the step of displaying the transmission rate to actually beassigned which is calculated before the communication path isestablished.
 7. A communication method in a system wherein each of datafor each of radio communication terminals is coded based on each of codekeys assigned to each of the radio communication terminals, each of thecoded data is stored into each of slots, a base station transmitsinformation in units of packet including the slots, the number of slotsincluded in the packet is predetermined, and each of the slots has acommunication information area which stores necessary variousinformation for indicating a state of the base station and for which theradio communication terminal connects to the base station, thecommunication method comprising: storing the code keys each of which isassigned to each of the radio communication terminals; receiving apacket transmitted from the base station when a communication path tothe base station is not established before a call connection request istransmitted to the base station; measuring whether each of all slots inthe received packet is an unused slot or a used slot by using the codedkeys each of which is assigned to each of the radio communicationterminals; measuring a parameter regarding a signal quality based on apilot signal of each of the slots and determining a request transmissionrate for the base station based on the measured parameter; and acquiringinformation, included in the communication information area, regardingthe number of mobile communication terminals connected to the basestation, calculating a transmission rate based on the number of usedslots, the number of unused slots, the request transmission rate and thenumber of radio communication terminals connected to the base stationbefore the communication path is established wherein the transmissionrate is a rate to be expected when the communication path to the basestation is established after the call connection request is transmittedto the base station.
 8. The communication method according to claim 7,further comprising the step of displaying the transmission rate toactually be assigned which is calculated before the communication pathis establish.